Abstract
Abstract. Above polar ice sheets, atmospheric water vapor exchange occurs across the planetary boundary layer (PBL) and is an important mechanism in a number of processes that affect the surface mass balance of the ice sheets. Yet, this exchange is not well understood and has substantial implications for modeling and remote sensing of the polar hydrologic cycle. Efforts to characterize the exchange face substantial logistical challenges including the remoteness of ice sheet field camps, extreme weather conditions, low humidity and temperature that limit the effectiveness of instruments, and dangers associated with flying manned aircraft at low altitudes. Here, we present an unmanned aerial vehicle (UAV) sampling platform for operation in extreme polar environments that is capable of sampling atmospheric water vapor for subsequent measurement of water isotopes. This system was deployed to the East Greenland Ice-core Project (EastGRIP) camp in northeast Greenland during summer 2019. Four sampling flight missions were completed. With a suite of atmospheric measurements aboard the UAV (temperature, humidity, pressure, GPS) we determine the height of the PBL using online algorithms, allowing for strategic decision-making by the pilot to sample water isotopes above and below the PBL. Water isotope data were measured by a Picarro L2130-i instrument using flasks of atmospheric air collected within the nose cone of the UAV. The internal repeatability for δD and δ18O was 2.8 ‰ and 0.45 ‰, respectively, which we also compared to independent EastGRIP tower-isotope data. Based on these results, we demonstrate the efficacy of this new UAV-isotope platform and present improvements to be utilized in future polar field campaigns. The system is also designed to be readily adaptable to other fields of study, such as measurement of carbon cycle gases or remote sensing of ground conditions.
Highlights
The Greenland and Antarctic ice sheets interact with the atmosphere through continuous exchange of water vapor by condensation and sublimation, as well as through precipitation events (Fettweis et al, 2020)
The standard water isotope data were analyzed on a continuous flow analysis (CFA) system adapted from Jones et al (2017a)
The data consist of measurements of hydrogen and oxygen isotopes in water vapor, where the ratio of heavy to light water isotopes in a sample is expressed in δ notation (Epstein et al, 1953; Mook and Rozanski, 2000) relative to internationally recognized primary reference materials Vienna Standard Mean Ocean Water (VSMOW) and normalized to Standard Light Antarctic Precipitation (SLAP) in accordance with IAEA reference material (2017): δsample =
Summary
The Greenland and Antarctic ice sheets interact with the atmosphere through continuous exchange of water vapor by condensation and sublimation, as well as through precipitation events (Fettweis et al, 2020). The exchange of water vapor between the ice sheet and different parts of the atmosphere has importance for varying fields of study, including (1) ice–atmosphere modeling and mixing processes, (2) ice sheet mass balance, (3) satellite detection algorithms, (4) moisture tracking, (5) ice core science, and (6) modeling of the hydrologic cycle in general. In each of these cases, a critical missing component is the reliable measurement of the water vapor flux across the PBL border with the free troposphere.
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